/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/

/*
 *  Elliptic curve DSA
 *
 *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *  This file is part of mbed TLS (https://tls.mbed.org)
 */

/*
 * References:
 *
 * SEC1 http://www.secg.org/index.php?action=secg,docs_secg
 */

#include "tls/config.h"

#if defined(MBEDTLS_ECDSA_C)

#include "tls/ecdsa.h"
#include "tls/asn1write.h"

#include <string.h>

#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
#include "tls/hmac_drbg.h"
#endif

/*
 * Derive a suitable integer for group grp from a buffer of length len
 * SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
 */
static int derive_mpi(const mbedtls_ecp_group *grp, mbedtls_mpi *x, const unsigned char *buf, size_t blen)
{
	int ret;
	size_t n_size = (grp->nbits + 7) / 8;
	size_t use_size = blen > n_size ? n_size : blen;

	MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(x, buf, use_size));
	if (use_size * 8 > grp->nbits) {
		MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(x, use_size * 8 - grp->nbits));
	}

	/* While at it, reduce modulo N */
	if (mbedtls_mpi_cmp_mpi(x, &grp->N) >= 0) {
		MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(x, x, &grp->N));
	}

cleanup:
	return (ret);
}

/*
 * Compute ECDSA signature of a hashed message (SEC1 4.1.3)
 * Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
 */
int mbedtls_ecdsa_sign(mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s, const mbedtls_mpi *d, const unsigned char *buf, size_t blen, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng)
{
	int ret, key_tries, sign_tries, blind_tries;
	mbedtls_ecp_point R;
	mbedtls_mpi k, e, t;

	/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
	if (grp->N.p == NULL) {
		return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
	}

	mbedtls_ecp_point_init(&R);
	mbedtls_mpi_init(&k);
	mbedtls_mpi_init(&e);
	mbedtls_mpi_init(&t);

	sign_tries = 0;
	do {
		/*
		 * Steps 1-3: generate a suitable ephemeral keypair
		 * and set r = xR mod n
		 */
		key_tries = 0;
		do {
			MBEDTLS_MPI_CHK(mbedtls_ecp_gen_keypair(grp, &k, &R, f_rng, p_rng));
			MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(r, &R.X, &grp->N));

			if (key_tries++ > 10) {
				ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
				goto cleanup;
			}
		} while (mbedtls_mpi_cmp_int(r, 0) == 0);

		/*
		 * Step 5: derive MPI from hashed message
		 */
		MBEDTLS_MPI_CHK(derive_mpi(grp, &e, buf, blen));

		/*
		 * Generate a random value to blind inv_mod in next step,
		 * avoiding a potential timing leak.
		 */
		blind_tries = 0;
		do {
			size_t n_size = (grp->nbits + 7) / 8;
			MBEDTLS_MPI_CHK(mbedtls_mpi_fill_random(&t, n_size, f_rng, p_rng));
			MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&t, 8 * n_size - grp->nbits));

			/* See mbedtls_ecp_gen_keypair() */
			if (++blind_tries > 30) {
				return (MBEDTLS_ERR_ECP_RANDOM_FAILED);
			}
		} while (mbedtls_mpi_cmp_int(&t, 1) < 0 || mbedtls_mpi_cmp_mpi(&t, &grp->N) >= 0);

		/*
		 * Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n
		 */
		MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(s, r, d));
		MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&e, &e, s));
		MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&e, &e, &t));
		MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&k, &k, &t));
		MBEDTLS_MPI_CHK(mbedtls_mpi_inv_mod(s, &k, &grp->N));
		MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(s, s, &e));
		MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(s, s, &grp->N));

		if (sign_tries++ > 10) {
			ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
			goto cleanup;
		}
	} while (mbedtls_mpi_cmp_int(s, 0) == 0);

cleanup:
	mbedtls_ecp_point_free(&R);
	mbedtls_mpi_free(&k);
	mbedtls_mpi_free(&e);
	mbedtls_mpi_free(&t);

	return (ret);
}

#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
/*
 * Deterministic signature wrapper
 */
int mbedtls_ecdsa_sign_det(mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s, const mbedtls_mpi *d, const unsigned char *buf, size_t blen, mbedtls_md_type_t md_alg)
{
	int ret;
	mbedtls_hmac_drbg_context rng_ctx;
	unsigned char data[2 * MBEDTLS_ECP_MAX_BYTES];
	size_t grp_len = (grp->nbits + 7) / 8;
	const mbedtls_md_info_t *md_info;
	mbedtls_mpi h;

	if ((md_info = mbedtls_md_info_from_type(md_alg)) == NULL) {
		return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
	}

	mbedtls_mpi_init(&h);
	mbedtls_hmac_drbg_init(&rng_ctx);

	/* Use private key and message hash (reduced) to initialize HMAC_DRBG */
	MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(d, data, grp_len));
	MBEDTLS_MPI_CHK(derive_mpi(grp, &h, buf, blen));
	MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&h, data + grp_len, grp_len));
	mbedtls_hmac_drbg_seed_buf(&rng_ctx, md_info, data, 2 * grp_len);

	ret = mbedtls_ecdsa_sign(grp, r, s, d, buf, blen, mbedtls_hmac_drbg_random, &rng_ctx);

cleanup:
	mbedtls_hmac_drbg_free(&rng_ctx);
	mbedtls_mpi_free(&h);

	return (ret);
}
#endif							/* MBEDTLS_ECDSA_DETERMINISTIC */

/*
 * Verify ECDSA signature of hashed message (SEC1 4.1.4)
 * Obviously, compared to SEC1 4.1.3, we skip step 2 (hash message)
 */
int mbedtls_ecdsa_verify(mbedtls_ecp_group *grp, const unsigned char *buf, size_t blen, const mbedtls_ecp_point *Q, const mbedtls_mpi *r, const mbedtls_mpi *s)
{
	int ret;
	mbedtls_mpi e, s_inv, u1, u2;
	mbedtls_ecp_point R;

	mbedtls_ecp_point_init(&R);
	mbedtls_mpi_init(&e);
	mbedtls_mpi_init(&s_inv);
	mbedtls_mpi_init(&u1);
	mbedtls_mpi_init(&u2);

	/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
	if (grp->N.p == NULL) {
		return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
	}

	/*
	 * Step 1: make sure r and s are in range 1..n-1
	 */
	if (mbedtls_mpi_cmp_int(r, 1) < 0 || mbedtls_mpi_cmp_mpi(r, &grp->N) >= 0 || mbedtls_mpi_cmp_int(s, 1) < 0 || mbedtls_mpi_cmp_mpi(s, &grp->N) >= 0) {
		ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
		goto cleanup;
	}

	/*
	 * Additional precaution: make sure Q is valid
	 */
	MBEDTLS_MPI_CHK(mbedtls_ecp_check_pubkey(grp, Q));

	/*
	 * Step 3: derive MPI from hashed message
	 */
	MBEDTLS_MPI_CHK(derive_mpi(grp, &e, buf, blen));

	/*
	 * Step 4: u1 = e / s mod n, u2 = r / s mod n
	 */
	MBEDTLS_MPI_CHK(mbedtls_mpi_inv_mod(&s_inv, s, &grp->N));

	MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&u1, &e, &s_inv));
	MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&u1, &u1, &grp->N));

	MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&u2, r, &s_inv));
	MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&u2, &u2, &grp->N));

	/*
	 * Step 5: R = u1 G + u2 Q
	 *
	 * Since we're not using any secret data, no need to pass a RNG to
	 * mbedtls_ecp_mul() for countermesures.
	 */
	MBEDTLS_MPI_CHK(mbedtls_ecp_muladd(grp, &R, &u1, &grp->G, &u2, Q));

	if (mbedtls_ecp_is_zero(&R)) {
		ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
		goto cleanup;
	}

	/*
	 * Step 6: convert xR to an integer (no-op)
	 * Step 7: reduce xR mod n (gives v)
	 */
	MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&R.X, &R.X, &grp->N));

	/*
	 * Step 8: check if v (that is, R.X) is equal to r
	 */
	if (mbedtls_mpi_cmp_mpi(&R.X, r) != 0) {
		ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
		goto cleanup;
	}

cleanup:
	mbedtls_ecp_point_free(&R);
	mbedtls_mpi_free(&e);
	mbedtls_mpi_free(&s_inv);
	mbedtls_mpi_free(&u1);
	mbedtls_mpi_free(&u2);

	return (ret);
}

/*
 * Convert a signature (given by context) to ASN.1
 */
int ecdsa_signature_to_asn1(const mbedtls_mpi *r, const mbedtls_mpi *s, unsigned char *sig, size_t *slen)
{
	int ret;
	unsigned char buf[MBEDTLS_ECDSA_MAX_LEN];
	unsigned char *p = buf + sizeof(buf);
	size_t len = 0;

	MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_mpi(&p, buf, s));
	MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_mpi(&p, buf, r));

	MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&p, buf, len));
	MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(&p, buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));

	memcpy(sig, p, len);
	*slen = len;

	return (0);
}

/*
 * Compute and write signature
 */
int mbedtls_ecdsa_write_signature(mbedtls_ecdsa_context *ctx, mbedtls_md_type_t md_alg, const unsigned char *hash, size_t hlen, unsigned char *sig, size_t *slen, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng)
{
	int ret;
	mbedtls_mpi r, s;

	mbedtls_mpi_init(&r);
	mbedtls_mpi_init(&s);

#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
	(void)f_rng;
	(void)p_rng;

	MBEDTLS_MPI_CHK(mbedtls_ecdsa_sign_det(&ctx->grp, &r, &s, &ctx->d, hash, hlen, md_alg));
#else
	(void)md_alg;

	MBEDTLS_MPI_CHK(mbedtls_ecdsa_sign(&ctx->grp, &r, &s, &ctx->d, hash, hlen, f_rng, p_rng));
#endif

	MBEDTLS_MPI_CHK(ecdsa_signature_to_asn1(&r, &s, sig, slen));

cleanup:
	mbedtls_mpi_free(&r);
	mbedtls_mpi_free(&s);

	return (ret);
}

#if ! defined(MBEDTLS_DEPRECATED_REMOVED) && \
	defined(MBEDTLS_ECDSA_DETERMINISTIC)
int mbedtls_ecdsa_write_signature_det(mbedtls_ecdsa_context *ctx, const unsigned char *hash, size_t hlen, unsigned char *sig, size_t *slen, mbedtls_md_type_t md_alg)
{
	return (mbedtls_ecdsa_write_signature(ctx, md_alg, hash, hlen, sig, slen, NULL, NULL));
}
#endif

/*
 * Read and check signature
 */
int mbedtls_ecdsa_read_signature(mbedtls_ecdsa_context *ctx, const unsigned char *hash, size_t hlen, const unsigned char *sig, size_t slen)
{
	int ret;
	unsigned char *p = (unsigned char *)sig;
	const unsigned char *end = sig + slen;
	size_t len;
	mbedtls_mpi r, s;

	mbedtls_mpi_init(&r);
	mbedtls_mpi_init(&s);

	if ((ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) != 0) {
		ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
		goto cleanup;
	}

	if (p + len != end) {
		ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
		goto cleanup;
	}

	if ((ret = mbedtls_asn1_get_mpi(&p, end, &r)) != 0 || (ret = mbedtls_asn1_get_mpi(&p, end, &s)) != 0) {
		ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
		goto cleanup;
	}

	if ((ret = mbedtls_ecdsa_verify(&ctx->grp, hash, hlen, &ctx->Q, &r, &s)) != 0) {
		goto cleanup;
	}

	if (p != end) {
		ret = MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH;
	}

cleanup:
	mbedtls_mpi_free(&r);
	mbedtls_mpi_free(&s);

	return (ret);
}

/*
 * Generate key pair
 */
int mbedtls_ecdsa_genkey(mbedtls_ecdsa_context *ctx, mbedtls_ecp_group_id gid, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng)
{
	return (mbedtls_ecp_group_load(&ctx->grp, gid) || mbedtls_ecp_gen_keypair(&ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng));
}

/*
 * Set context from an mbedtls_ecp_keypair
 */
int mbedtls_ecdsa_from_keypair(mbedtls_ecdsa_context *ctx, const mbedtls_ecp_keypair *key)
{
	int ret;

	if ((ret = mbedtls_ecp_group_copy(&ctx->grp, &key->grp)) != 0 || (ret = mbedtls_mpi_copy(&ctx->d, &key->d)) != 0 || (ret = mbedtls_ecp_copy(&ctx->Q, &key->Q)) != 0) {
		mbedtls_ecdsa_free(ctx);
	}

	return (ret);
}

/*
 * Initialize context
 */
void mbedtls_ecdsa_init(mbedtls_ecdsa_context *ctx)
{
	mbedtls_ecp_keypair_init(ctx);
}

/*
 * Free context
 */
void mbedtls_ecdsa_free(mbedtls_ecdsa_context *ctx)
{
	mbedtls_ecp_keypair_free(ctx);
}

#endif							/* MBEDTLS_ECDSA_C */
